flathead oil pressure senders
 

can anyone explain why an 80# oil sender would not work in all flatheads and what the diff is between the 80 and 50 in practical terms? i have interchanged these over the years with no issues and haven't spent much time thinking about it.

Re: flathead oil pressure senders
 

I strongly suspect the different "senders" have different electrical resistance. The sender regulates the current seen by the oil pressure guage. The resistance of the sender would have to be matched to the gauge to get an accurate reading. If I'm wrong, hopefully someone will correct this post - and earn my thanks at the same time.

Re: flathead oil pressure senders
 

i contacted a supplier that said they sell 80# senders for all 35-53 flatheads but i am still unsure.

Re: flathead oil pressure senders
 

35-41 use a 50# sender which is difficult to find.I had an 80# sender in my 35 and it did not read correctly.When I found the 50# and changed it ,all was good.I suppose the guage and sender should be compatible.

Re: flathead oil pressure senders
 

The 80# will work, but calibration will be wrong. I'm not sure which, but you'll get either .625 x or 1.6 x the correct reading.

There were two identifying features for a 50# sender, either it was marked 50, or had no mark at all. All 80# senders are so marked.

Re: flathead oil pressure senders
 

Does anyone know this second statement by 38 is definately correct were some 50's NOT marked?? ken ct.:)

Re: flathead oil pressure senders
 

i have 2 of these senders left and neither are marked. one came out of my 53 merc motor and one was on my 40 ford motor and they look identical and neither have any marking except for a very small circled number or symbol that looks like a 2.

Re: flathead oil pressure senders
 

Original '35 - '41 senders were not marked. When the 80# senders came in, there was the need to identify the difference, so from that point forward, all senders were marked, at least while the 50's were still being supplied.

F1builder has now thrown a monkey wrench into the discussion, so maybe someone can pick it up from here?

Re: flathead oil pressure senders
 

I agree with ford38v8 that from my experance the early 50# was not marked. I have not seen a 80# unmarked. I also believe the 50# sender was marked upon the introduction of the 80#. It is possible the unmarked sender out of a 53 Merc is a 50# and installed inproperly to give a higher oil pressure reading on the gauge.

Re: flathead oil pressure senders
 

I agree you need to match the sender scale with the gauge scale. A 50# sender must be used with a 50# gauge and the same with the 80#s. However, I did find that a sender for a 302 in a 1980 F100 does work accurately with the stock 50# guage in my pickup. The sender I was sold for the application is a Standard Motor Products partno PS-60. 3 years ago it cost $25.00, available locally and was made in the USA.

Re: flathead oil pressure senders
 

Different senders have different ohms ranges, that is true. Senders must match the gauge. Henry / Kokomo is right on this.

Re: flathead oil pressure senders
 

Possibly "KS," the trademark of King-Seeley who made these units?

Re: flathead oil pressure senders
 

No telling how many "aftermarket" senders were made or whether they were all marked with the psi rating. If they were made by King Seeley they generally always have the trade mark KS in a circle stamped on there.

Kerby

Re: flathead oil pressure senders
 

Are you running 12 volts neg ground?

Re: flathead oil pressure senders
 

There is a commercially available sending unit that can replace the original 50# sender and works correctly with a 50# gauge. I believe it is/was used on a Jeep/AMC product. I have this info saved in my computer files which I do not have access to at the moment but could post later if anyone is interested.

Re: flathead oil pressure senders
 

John,
Please post the Jeep/AMC part number for the oil pressure sending unit. Thanks!

Re: flathead oil pressure senders
 

I got one from Kaiser Willys Auto Supply for my '40 pickup, but I have no part #. $36.74

Re: flathead oil pressure senders
 

BrianCT,

Yes the system was converted to 12v neg ground, I am running the stock gauges using a 6v Runtz reducer on each. The gauge and sender will operate the same way on either polarity as long as only 6v is applied.

Re: flathead oil pressure senders
 

Ive looked up the jeep unit in the past,it obviously works but not quite a duplicate of the original. Its taller i remember so would not look right if going for points for those of you who care about that stuff.Probebly a point deduction on it. For me i wouldn't care a hoot. ken ct. This was a good thread,maybe we all learned something.

Re: flathead oil pressure senders
 

F1builder,
Here is an attempt to answer your original question. From what I've observed by exploring a number of the Ford indicator systems is the gauge units are basically the same. Meaning it takes the same electrical energy to move the pointer from 0 to full scale. The pointer is moved by putting current through a heater wire wrapped around a bi-mettalic arm. More current equals more pointer deflection. The original senders use a similar heater wire bi-metallic strip. The strip is attached to a set of points. One side of these points is tied to the sensor element. In the case of the OP it is a diaphram. The diaphram actually establishes the range for the sensor. So if a 80# sensor is used with the 50# gauge when the sensor sees 50# the guage will show about 30#. Inversely a 50# sensor seeing 50# will show 80# on an 80# gauge.

Sorry this got a little long.